“oomis – Why only by a je will he think cheap jew more than saying it by a non jew? “
First of all, and most obvious, he will not think to himself, “Cheap Jew,” if it is a non-Jew to whom he is delivering, because he will see it is a non-Jew. He might think to himself “Cheap jerk!” But when it is clearly a JEW, it does not need anything more than that Jewishness for him to blame that perceived cheapness on the money-grubbing Jews. Since when do our enemies EVER need an excuse to call us (fill in the blank)_______________ Jew!
So why would you deliberately want to cause such a chillul, forgetting for the moment that in fact, is is a nice thing to show hakoras hatov to ANYONE who delivers something to you or performs a service. Being that he is employed no doubt at fairly low wages, money is the best hakoras hatov.